Abstract
Hopping provides efficient and energy saving locomotion for kangaroos, but it results in great forces in the knee joints. A previous study has suggested that a unique fibrous cartilage in the central region of the tibial cartilage could serve to decrease the peak stresses generated within kangaroo tibiofemoral joints. However, the influences of the microstructure, composition and mechanical properties of the central fibrous and peripheral hyaline cartilage on the function of the knee joints are still to be defined. The present study showed that the fibrous cartilage was thicker and had a lower chondrocyte density than the hyaline cartilage. Despite having a higher PG content in the middle and deep zones, the fibrous cartilage had an inferior compressive strength compared to the peripheral hyaline cartilage. The fibrous cartilage had a complex three dimensional collagen meshwork with collagen bundles parallel to the surface in the superficial zone, and with collagen bundles both parallel and perpendicular to the surface in the middle and deep zones. The collagen in the hyaline cartilage displayed a typical Benninghoff structure, with collagen fibres parallel to the surface in the superficial zone and collagen fibres perpendicular to the surface in the deep zone. Elastin fibres were found throughout the entire tissue depth of the fibrous cartilage and displayed a similar alignment to the adjacent collagen bundles. In comparison, the elastin fibres in the hyaline cartilage were confined within the superficial zone. This study examined for the first time the fibrillary structure, PG content and compressive properties of the central fibrous cartilage pad and peripheral hyaline cartilage within the kangaroo medial tibial plateau. It provided insights into the microstructure and composition of the fibrous and peripheral hyaline cartilage in relation to the unique mechanical properties of the tissues to provide for the normal activities of kangaroos.
Highlights
The locomotory characteristics of kangaroos are unusual, with gait parameters differing from those of humans and quadrupedal running mammals
The current study examined in detail the microstructure, composition and mechanical properties of the central fibrous cartilage and peripheral hyaline cartilage of the medial tibia of kangaroo
This study found that the fibrous cartilage articulating directly with the distal femoral condyle was thicker than the periphery hyaline cartilage covered by meniscus
Summary
The locomotory characteristics of kangaroos are unusual, with gait parameters differing from those of humans and quadrupedal running mammals. Kangaroos lift off and land on the ground simultaneously with both feet This unusual form of locomotion results in high ground reaction forces and high loads in the kangaroo knee joints [2]. A previous study has reported that kangaroo tibia possess an unusual fibrous cartilage pad in the centre, which was surrounded by hyaline cartilage [2] Such a unique tibial anatomy has been suggested to be crucial for the kangaroo knee to adapt to the prevailing high loads and speed requirements during the locomotion [2]. The fibrous pad has been reported to be softer and more compressible than the surrounding hyaline cartilage This enabled the pad to deform more to enlarge the articular contact area, decreasing the high frequent peak stresses generated in the knee. Detailed study of the compositional, microstructural and mechanical characteristics of the fibrous cartilage and the peripheral hyaline cartilage will offer greater understanding of the unique function of the fibrous pad and kangaroo tibial plateau in the animal’s locomotion The study examined the structural arrangement of collagen and elastin fibres, PG content and mechanical properties of the fibrous and hyaline cartilage in the medial tibia of kangaroo knees
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